Abstract:
In this paper, the adsorption and adsorption mechanism of poly(acrylic acid) (PAA) and citric acid (CA) on the surface of calcium sulfate hemihydrate (HCS) were studied using organic carboxylic acids as additives. The adsorption characteristics of additives on HCS surface were analyzed by using total organic carbon analyser (TOC). TEM-EELS, X-ray electron spectroscopy (XPS), laser Raman spectroscopy, FTIR and other characterization methods were used to analyze the adsorption layer structure. Finally, the adsorption mechanism of additives was explored in combination with the crystal structure of HCS. The results show that the adsorption of organic carboxylic acid on the surface of HCS can be fitted by the Langmuir isotherm adsorption theory, and the adsorption kinetics was found to follow the second-order rate equation. Organic carboxylic acid was absorbed on the surface of gypsum through the interaction between carboxyl group and Ca
2+. The carboxyl group of CA was preferentially adsorbed in the C-axis direction of the HCS crystal compared to crystal planes in other directions. PAA was adsorbed on each crystal surface of HCS, and it exerts a dispersion effect through electrostatic repulsion and steric hindrance, which in turn affects the crystal morphology. At the same time, taking CA as an example, the stability constants of the complexes adsorbed on the surface of HCS were studied.